Fast Tests Are Latest Weapons Against Infections

A new lab test could quickly detect methicillin-resistant Staphylococcus aureus, or MRSA, bacteria like these in the blood.

Janice Carr
/ CDC

Originally published on June 29, 2012 7:42 pm

Show up at the emergency room or your doctor's office with symptoms of a serious infection, and there's a good chance you'll get an antibiotic. You might even get a few.

But antibiotics don't work on viruses. And a particular antibiotic may be suited for one kind of germ, but not another.

The problem for your doctor — and you — is that it can take days to grow enough of the germs afflicting you to identify them conclusively using traditional tests. And if you're really sick, the doctor may try a bunch of antibiotics right away, just to be sure one of them starts getting you back on the road to health.

"We've been using agar plates, and we've been sort of in the dark ages," says David Gilbert, chief of infectious diseases at Providence Portland Medical Center in Oregon. "We're forced to guess what's there."

Faster, more specific tests would help. And the Food and Drug Administration has recently approved some. This week, while you might have been distracted by the Supreme Court, the agency cleared a test for a dozen bacteria that cause infections in the blood.

"Bloodstream infections are always treated with antimicrobial drugs, and it is essential to identify which antimicrobial drug is appropriate for a specific patient as quickly as possible," FDA's Alberto Gutierrez said in a statement. "This new test is an important tool that will help physicians treat patients quickly with the correct antibiotics."

The test, made by Nanosphere, works in a few hours instead of days. It fingerprints the germs' DNA and can even detect when the bugs carry genes that render them resistant to some antibiotics. The test costs less than $100.

The FDA gave the green light to another Nanosphere test for respiratory viruses last year. A company called Idaho Technology has a one-hour test for respiratory viruses, too.

These options, and others in the works, should be helpful, Gilbert tells Shots. Fast, specific results can help guide treatment and spare the use of antibiotics that wouldn't work.

Overuse of antibiotics is one factor in the rise of antibiotic-resistant bacteria. "We're running out of antibiotics," he says. "It's very important that we preserve our current inventory of drugs."

Update 8:28 p.m.: Like most things in medicine, these new molecular tests have their weaknesses. Marya Zilberberg, a Massachusetts doctor who is a stickler for the evidence, explains how even these very sensitive and very specific tests can still lead doctors astray.